This paper presents experimental results associated with the human factors aspects of using color contours to visualize electric power system bus voltage magnitude information. Participants were divided into three groups: the first group only one-line numeric data, the second only one-line contour data, while the third saw both. The purpose of the experiment was to determine how quickly participants could both acknowledge low voltage violations and perform corrective control actions. Results indicated the contour only visualization resulted in the quickest voltage violation acknowledgements, while the numeric data only visualization resulted in the quickest solution times. Testing was done using a modified version of the IEEE 118 bus system.